On 9/30/2006 10:39 AM, Martin Maechler wrote: >>>>>> "Herve" == Herve Pages <[EMAIL PROTECTED]> >>>>>> on Fri, 29 Sep 2006 18:06:41 -0700 writes: > > Herve> Hi, > Herve> This looks like a bug: > hmm, maybe... > or maybe not; I vaguely recall that this is documented somewhere... > > >> a <- list(b=5) > >> a[['b']] > Herve> [1] 5 > >> a[[t<-'b']] > > Herve> Nothing gets printed! > > Yes, but that is not really much related to "[[" > but rather to "<-" which momentarily turns off auto-printing.
I think this is probably not intentional, because the behaviour is so inconsistent. In names.c, the "eval" entry for "[" and "[[" is 0, which is supposed to indicate R_Visible is on. It's the same as for c(), substitute(), quote(), interactive(), expression(), nargs(), and those return a visible result. On the other hand, dim(), dimnames(), as.character(), call(), rep(), seq.int(), seq_along() also have eval=0, and they give an invisible result. Among the eval=10 functions, I see visible results from unlist(), cbind(), rbind(), and invisible ones from sys.parent(), sys.call() etc., parent.frame(), and so on (I gave up testing at this point). I suspect the problem is that these are low level functions where the evaluator does almost nothing automatically, and handling R_Visible was just overlooked. Duncan Murdoch > > Similar things happen in many similar circumstances. > > Herve> I need to use parenthesis to see the expected result: > > >> a[[(t<-'b')]] > Herve> [1] 5 > > Herve> Cheers, > Herve> H. > > Martin > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
